In areas where different Third Generation Partnership Project (3GPP) access networks overlap or are adjacent to one another, when a subscriber changes an access system, for example, changes from a GSM/EDGE Radio Access Network/UMTS Terrestrial Radio Access Network (GERAN/UTRAN) to an Evolved UMTS Terrestrial Radio Access Network (EUTRAN), or from the EUTRAN to the GERAN/UTRAN, the subscriber needs to initiate a location update process, which brings certain load to the core network and air interfaces. In order to avoid such signaling load and to optimize the mobility management mechanism among different 3GPP access systems, the 3GPP has proposed an ISR mechanism in an idle mode, which aims at reducing the signaling load caused by the mobility management process of a user equipment (UE) among different access networks. The UE is registered with a serving general packet radio service support node (SGSN) and a mobility management entity (MME) in sequence, and then the ISR is enabled. Thus, as long as the UE does not leave the Routing Area (RA) and Tracking Area (TA) where it is located at the time of registering with the SGSN and MME, the UE does not need to initiate the location update process. Thus, even though a mobile subscriber is frequently handed over between a 2G/3G cell and a Long Term Evolution (LTE) cell, no signaling load will be generated. In addition, even if the RA or TA where the subscriber is located is changed, as long as the SGSN and MME where the subscriber is registered are not changed, the TA or RA update process initiated by the UE does not need to re-register the SGSN or MME on a Home Subscriber Server (HSS). Furthermore, in order to ensure that the MT (Mobile Terminated) service of the subscriber is not influenced, a Serving Gateway (SGW) needs to mark subscribers with the ISR enabled. When receiving downlink data or signaling of such a subscriber, the SGW notifies both the SGSN and the MME to initiate paging at the same time, thereby ensuring that the subscriber can be paged.
In the implementation of the present invention, the inventors found at least the following problem in the prior art, that is, when the UE is handed over between networks, the ISR status of the UE cannot be processed.